Time-delayed undervoltage trippingmechanism for circuit breakers



2, J. w. TIMEDELAYED UNDERVOLTAGE TRIRPING-MECHANISM FOR CIRCUIT-B REAKERS Filed May 9 1940. 2 sheets-Sheet 1 SYM ATTORNEY Patented Feb. 2, 1943 TIME-DELAYED UNDERVOLTAGE TRIPPING- MECHANISM FOR CIRCUIT BREAKERS John W. May, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 9, 1940, Serial No. 334,182

6 Claims.

My invention relates to time-delayed undervoltage tripping-mechanisms for circuit-breakers, and it has particular relation to such devices utilizing a suction-type or sucker-type dashpot in combination with a clapper-type undervoltage electromagnet.

An object of my invention is to provide a novel lost-motion connecting-means between the movable armature-arm of the electromagnet and the plunger of the dashpot in order to obtain proper action of both the dashpot and the electromagnet, without the necessity for exact niceties in the design, and bearing in mind the necessity for avoiding any lateral or twisting reactions on the stem of the dashpot-plunger, and recognizing the fact that both the dashpot-plunger and the electromagnet-armature must be seated securely on their respective frames, in order to develop the intended forces.

While my invention was designed particularly for utilization in connection with air-type circuit-breakers, and while it is so illustrated in the accompanying drawings, I wish it to be understood that the invention, in its broader aspects, is not limited to any particular type of circuitbreaker.

In the drawings:

Figure 1 is a sectional side-elevational view, not precisely to scale, but showing the general principles of an illustrative kind of circuitbreaker and circuit-breaker operating-mechanism, embodying a preferred form of embodiment of my improved undervoltage mechanism, the section-plane being approximately indicated by the line I-I in Fig. 2, and the operatinghandle having been removed,

Fig. 2 is a front-elevational view of a S-pole breaker embodying my invention,

Fig. 3 is a cross-sectional view on approximately the plane indicated by the line III-III in Fig. 2, showing a side elevation of my improved undervoltage mechanism, the drawings being not precisely to scale, but illustrating the general principles of my improved mechanism, and

Fig. 4 is a front-elevational View of the undervoltage mechanism shown in Fig. 3.

My invention is illustrated in connection with an air-type circuit breaker which is illustrated as being mounted upon an insulating panel 5 and comprising two main stationary contact-members 8 and 'I (Fig. 1) which are bridged by a movable contact-member 8 carried by a movable contact-arm 9 which is pivoted at II on a stationary frame-member I2 (Figs. 1 and 2) carried by the panel 5. The main contacts 6 8--1 are supplemented by auxiliary contacts I3 (Fig. 1) and also by arcing-contacts I4, associated with an arc-chute structure which is diagrammatically indicated at I5 (Figs. 1 and 2). The particular circuit-breaker which I have illustrated utilizes a contact-system which is described and claimed in a patent of Leon R. Ludwig and Merl E. Horn, No. 2,144,471, granted September 10, 1940, and assigned to the Westinghouse Electric & Manufacturing Company; while the illustrated arc-extinguishing structure I5 may be that which is described and claimed in an application oi Leon R. Ludwig, Serial No. 216,884, iiled July l, 1938, and assigned to the Westinghouse Electric & Manufacturing Company, which application became Patent No. 2,243,038 on May 20, 1941.

In Fig. 1, I have illustrated a circuit-breaker mechanism which is substantially that which is described and claimed in an Austin Patent No. 2,177,014, granted October 24, 1939.

As shown in Fig. 1, the movable contact-arm il is normally biased toward an open position by means ci an accelerating or opening spring I6, which is connected between a point I'I on the breaker-arm 9 and a point I8 on the frame I2. The movable contact-arm 9 of the breaker is also connected, by means of a pivoted link 20, toa pin 2I carried by a toggle-lever 22 (Figs. 1 and 2).

The toggle-lever 22 is pivoted on a stationary pivot 23 (Fig. 1) carried by the frame I2, and it is shaped and arranged so as to carry two other pivot-pins 24 and 25, in addition to pivot-pin 2|, as well as having two depressions or spring-seats 2S and 27, a cam-surface 23, and an attachmentpoint 29 for an opening-spring or acceleratingspring 3i, the other end of which is connected to a xed pivot 32 carried by the frame I2. The toggle-lever 22 may also be provided with an air bumper 33, as illustrated.

The toggle-lever 22 is operatively associated with a closing lever 34 (Figs. 1 and 2) which is independently pivoted upon the same stationary pivot 23 (Fig. 1). The closing lever 34 carries a pin 35 which is provided with a roller 36 (Fig. 1) and it is also connected to a cross-bar 31 (Figs. l, 2 and 3) which extends transversely across the breaker-mechanism.

The toggle-lever 22 and the closing lever 34 are adapted to be releasably held together or interlocked, by means of a trigger latch 38 (Fig. I) which is carried by the pivot-pin 25 on the toggle-lever 22. The front end of the trigger latch 38 is provided with a latching surface 39 which abuts against the roller 36 of the closing lever 34, and the rear end of the trigger latch 38 carries a roller 4| which is normally latched or engaged by the end 42 of a roller trigger 43. The roller trigger 43 is carried by the pivot-pin 24 of the toggle-lever 22 and is provided with a depending arm 44 which may be actuated in order to trip or release the roller trigger 43 from the roller 4I of the trigger latch 38. When the trigger-latch 38 is in its latched position, as shown in Fig. 1, it operatively ties thetogglelever 22 to the closing lever 34 so that they will be held together.

The closing lever 34 is normally retained in its illustrated closed position, that is, when the circuit-breaker is closed, by means of a trigger or other releasable holding-means 45 which is pivotally carried by the stationary pivot 32, and which is provided with a shoulder 46 which engages the roller 36 of the closing lever 34, so as to prevent the latter from opening. The trigger 45 is'also provided with a cam-surface 41 which is adapted to be engaged by the cam surface 28 of jthe toggle-lever 22 whenl the toggle-lever opens, as will be subsequently described, thus releasing the trigger-shoulder 46 from its engagement with the roller 36 of the closing lever 34.

The release of the roller trigger 43 is effected by means of a tripping lever 58 (Fig. 1) which is carried by the stationary pivot-pin 32. The tripm ping lever 59 is provided with a shoulder 5| which is adapted to engage the depending arm 44 of the roller trigger 43 so as to actuate said roller trigger against the bias of a spring 52 which is seated in the depression 26 of the toggle-lever 22. The actuation of the roller trigger 43 lifts its abutment-end 42 out of engagement with the roller 4l of the trigger latch 38, so that the force of the powerful opening-spring 3l of the togglelever 22 will operate on the trigger latch 38 along a line joining the pivot-pin 25 with the abutment-end 39 of the trigger latch, this line of 'action being slightly off-center with respect to the line joining the pivot-pins 25 and 35, so that the trigger latch 38 will be kicked oi of the roller l36 of the closing lever 34 as soon as its own roller 4|-is Yreleasedby the roller trigger 43. The trigger latch 38 is provided with a light relatchingspring 53 which is seated in the depression 21 in the toggle-lever 22.

The tripping lever 58 and the trigger 45 are joined by means of a spring 54 which serves to bias the trigger 45 toward its latching position,

With'its latching-shoulder 46 in engagement with 1 the roller 36 of the closing lever 34. 'Ihe spring 54 also biases the tripping lever 58 toward its non-tripping position in engagement with a spring-stop 55. The tripping lever 56 is provided, at `one end, with a transversely extending actuating arm 56 (Figs. l and 3), while its other end is connected to a trip-bar 51 (Figs. 1 and 2).

The bottom stationary contact-member 1 (Fig. 1) isconnected in series with a series trip-coil 58 which-is operative, when the current reaches a predetermined magnitude, to elevate an armature 59 carrying a trip-pin 68 which engages the actuating arm 56 of the tripping lever 58, so as to elevate the tripping shoulder into engagement with the depending arm 44Y of the roller trigger 43, so as to release the trigger latch 36.

The circuit-breaker contact-structure and operating-me'chanism thus far described is usually a part of a multiple-pole construction such as is shown in Fig. 2, wherein a 3-pole breaker is 75 shown, with the dierent poles separated by barriers 6| and 52. Each pole is provided with its own toggle-lever 22 and closing lever 84, together with the necessary latching means therefor, but the cross-bar 31 .is common to all three poles, and the trip-bar 51 is also common to all three poles. The cross-bar 31 of Fig. 2 is provided with a closing-handle or operating-handle 63. A common trip-handle 64 may be provided on the tripbar 51, as indicated in Fig. 2..

My improved undervoltage mechanism is disposed at the right-hand end of the circuitbreaker as viewed in Fig. 2. It is shown in detail in Figs. 3 and 4. Essentially, it is a time-delayed drop-out clapper-type electromagnet or controlling-means which is adapted to drop out to a non-actuated position when the electromagnetic force developed therein falls below a predetermined minimum value. It is illustrated as comprising a U-shaped electromagnet-frame 66, the back of. which is mounted on the panel 5. One leg of the electromagnet-frame 66 is provided with a coil 61 for normally energizing the undervoltage mechanism in accordance with a predetermined response to a predetermined voltage, usually the voltage -of the line to which the circuit-breaker is connected. The two legs or polepieces of the electromagnet-frame 66 are adapted to be bridged by a movable armature 68 which is carried by a main lever or movable armaturearm 69 which is pivoted on a Xed pivot 1| carried by an extension of the electromagnet frame 66. v f

The main lever or movable armature-arm 69, besides carrying the magnetizable armature 66, is provided with a lug 13 carrying a pin 14 to which a biasing-spring 15 is connected, the other end of the biasing-spring being secured at a point 16 on an extension 0f the electromagnetvframe 66 in such position that the line of action of the spring, between the points 14 and 16, is slightly below the center of the main-lever pivot 1|, in the seated position of the armature 68, so thatl the biasing-spring 15 develops a relatively ,weak biasing-moment, tending to turn the movable armature-arm 69 clockwise, in an opening or dropping-out direction, as long as the armature 68 is seated against the pole-faces or abutments of the electromagnet-frame 66, said biasing force increasing rapidly in magnitude as the armature 68 moves away from the electromagnet frame 66, thus causing the armaturearm 69 to y open rapidly, when once its opening movement is started by a full or material separation of the armature 68 from the poleface portions of the electromagnet-frame 66. This biasing force can be adjusted by means of a vertical adjustment of the fixed spring-fastening 16, as indicated at 11.

The main lever or movable armature-arm 69, in addition to carrying the armature 68 and the spring-terminal 14, is also provided with a shoulder 18, an upwardly bent arm 19, and a downwardly extending arm 88. The upwardly bent arm 19 is connected, by means of a pivoted link 82, to an undervoltage trip-lever 83 which is pivoted on a fixed pivot 84 carried by the electromagnet-frame 66. The undervoltage trip-lever 83 is provided with an adjustable bumper or projection 85 which is adapted to engage the laterally extending actuating arm or cross-piece 55 of the circuit-breaker tripping lever 58 to elevate the latter in response to the flying-open movement of the armature-arm 69.

Means are provided for automatically retrieving the armature 68, or returning it to its seated position in engagement `with the electromagnetframe 96, in response to an opening movement of lcertain parts of the circuit-breaker mechanism. This armature-retrieving means includes a reset-lever 81 which is pivoted on the xed pivot 1|. The reset-lever 81 is provided with a shoulder 88 which is adapted, at; times, to abut against the shoulder 18 of the movable armaturearm 69. The reset-lever 81 is also provided with an upwardly extending arm-portion 99 which carries a terminal-connection 9| of a strong resetting-spring 92, the other end of which is carried by a fixed point 93 in an extension of the electromagnet-frame 69. The eiTect of the resetting-spring 92 is to strongly bias the resetlever 81 in a clockwise, or resetting, direction, so that, if the resetting-spring 92 has its way, it will force the reset-shoulder 88 against the armature-arm shoulder 18 with a force strong enough to reset or reseat the armature 68 against the bias of its opening or drop-out spring 15.

The reset-lever 81 is `also provided with an outwardly extending arm 95 which carries a pivot-pin 96 to which is attached a substantially vertical link 91 terminating in a pin 98 which rises in a substantially vertical slot 99 in a bracket |99 carried by the cross-bar 31 of the closing levers 34 of the circuit-breaker mechanism. Whenever the circuit-breaker is in its closed positon, the linkage-pin 98 rests in the top of the slot 99 and causes the vertical link 91 to press the reset arm 95 downwardly, so as to hold the reset shoulder 88 out of engagement with the movable armature-arm B9 of the undervoltage tripping-mechanism, leaving the movable armature-arm 69 free to ily open when the forces operating upon the armature-arm have a suitable resultant component in the opening direction.

After the circuit-breaker has tripped to an open-circuiting position of its movable contactarm 9 (Fig. 1), and before the movable contactarm can be reclosed, the closing lever 34 will be moved in an opening direction in which the cross-bar 31 is elevated, this operation being performed either automatically or, as illustrated, by an elevation of the handle 63 (Fig. 2). The vertical link 91 and the slotted bracket |99 of the undervoltage-mechanism (Fig. 3) constitute a lost-motion mechanical coupling-means for the reset-lever 81 whereby, when the cross-bar 31 begins to move upwardly, in its opening movement, the reset-lever 81 at rst moves with it, under the impulse of its resetting-spring 92, so as to forcibly or mechanically return the movable armature-arm 69 to its closed position in which the armature 68 is properly seated upon the pole-pieces of the electromagnet-frame 99. The lost-motion-coupling means is such, however, that after the armature 89 has been seated, so that the resetting-spring 92 can no longer move the reset-lever 81 in the counterclockwise or resetting direction, the cross-bar 31 of the closing levers 34 (Fig. l) may still continue through the final portion of its opening movement, during which time the linkage-pin 99 slides down through the slot 99 of the bracket |99, or rather the bracket |99 continues to move upwardly while the linkage-pin 98 remains still.

When the cross-bar 31 of the reclosing levers 34 is forced downwardly, during the closing movement of the actuating-mechanism of the circuit-breaker, it at rst has a loose connection with the undervoltage-mechanism, while the linkage-pin 98 rises in the slot 99, but the final closing-movement of the breaker-mechanism forces the reset-lever 81 downwardly, so that its shoulder 89 moves away from the cooperating 5 shoulder 18 on the movable armature-arm 69, during the last portion of the closing-movement of the breaker-mechanism, it being contemplated that the electromagnet-coil 61 of the undervoltage-mechanism will meanwhile have been energized, so that the electromagnetically developed force will hold the armature 93 in engagement with the electromagnet-rame 65 when the resetlever S1 moves out of engagement with the armature-arm 69.

The above-described mechanical resetting of the armature 98 is necessary, because a clappertype undervoltage magnet or relay, such as I utilize, does not usually develop a suilicient electromagnetic pull, under normal excitation-conditions, to attract the armature 98 to the electromagnet-frame 6G except when the armature is close to the pole-pieces of the frame.

n accordance with my invention, as shown in Fig. 3, the bottom depending arm 89 of the movable armature-arm 69 of the undervoltageresponsive mechanism is cooperatively associated with a dashpot |92 which operates as a time-delay means for delaying the `early stages of the opening movement of the armature-arm B9. The dashpot itself is of the suction-type in which the bottom surface of a movable plunger |99 is adapted to be normally seated in substantially contacting-engagement with the stationary top surface of the bottom member |94 of the dashpot, the dashpot being preferably partially filled with oil |95. As a result of this construction, a substantial force is required, which must be maintained for a certain predetermined interval of time, in order to separate the seating surfaces |93 and Hill. The dashpot usually embodies means for adjusting the operating-force and the time oi operation. This adjusting means may be of any desired type, ybut has nothing to do with present invention, a desirable means to that end being shown, however, in the Austin Patent No. l,5'78,572, granted March 30, i925.

in accordance with my invention, a novel looseconnection means is also utilized for the operative connection. between the vertical plungerrod |99 of the dashpot and the depending end S9 of the movable armature-arm 59 of the undervoltage-magne he upper end of the plungerrod 95 is provided wth a pivot-pin |91 carrying a roller 99 which is adapted to be engaged by the upper end-surface |99 of the main-lever` arm 99 when the main lever or armature-arm 69 moves a very slight amount away from the fully seated engagement of the armature 59 with the electromagnet-frame In accordance with my invention, the upper surface |99 of said depending arm 89 is so that it reacts in a substantially exactly tert al direction against the roller 5&9 by the plunger-rod |96, or in a direction which is substantially normal, or right angles, to the substantially contacting :u'faces |913. This provision is ...y slight lateral force, or rocking connec on means whereby both the agifiet-ar--ature 98 and the dashpot- |93 may be seated, against their respective contacting surfaces, with a slight lost-motion between them, so that it is not necessary to Vso finely adjust the manufacturing tolerances of the apparatus -that both of these parts will become seated at the same instant during the resetting movement of the electromagnet-mechanism.

In the particular form of my invention which is illustrated in Figs. 3 and 4, the bottom surface III of the depending end 80 of the armaturearm 59 moves downwardly, during the closing or resetting movement of the armature-arm 69, and in the very last stage of this closing-movement, it presses against the top of a slidable sleeve II2 on the plunger-rod |06 and forces said slidable sleeve downwardly so as to compress a spring I I3 which is disposed between said slidable sleeve I I2 and a fixed collar I I4 on the plunger-rod |06.

The result of the foregoing design is that the nal movement of the armature-arm 03, in the closing direction, depresses the bottom end of the arm 80 a slight distance down below the liftingroller |08 of the plunger-rod |06, so as to provide a loose-connection means such that, when the armature 68 is seated, the two substantially contacting suction-surfaces |03 and |04 are yieldably pressed vtogether by the spring I I3. On the other hand, when a predetermined reduction in the applied voltage or current in the magnetcoil G'I causes the biasing-spring I5 to begin to move the armature-arm 69 a very slight amount away from the full seated engagement of the armature 68 on the electromagnet-frame 66, the slight initial separation between the surface |09 and the roller |08 Will be taken up, so that the suction between the substantially contacting surfaces I03 and |04 of the dashpot will restrain any further or substantial opening-movement of the armature arm 69 until the suction-action is substantially broken at the suction-surfaces I03 and |04.

The object of this time-delay action, which prevents the armature 68 from becoming substantially or materially separated from its electromagnet-frame 66 for a certain time-delay delterrnined by the dashpot, is to render the undervoltage-mechanism unresponsive to voltage-dips of momentary or predeterminedly brief duration by temporarily holding the armature 68 so close to the electromagnet-frame 66 that the electromagnetic pull will be able to grip the armature upon the restoration of normal voltage-conditions. Thus, the circuit breaker will not be unnecessarily tripped open, in response to voltagedrops of such brief duration as to be unimportant from an operational standpoint with respect to the electrical system in which the circuit breaker is connected.

While I have described my invention in com bination with a certain type of circuit-breaker and a certain type of operating-mechanism therefor, and while I have described certain details of the undervoltage relay or magnet, and the dashpot, and the mechanical connectingmeans between the undervoltage armature-arm 69 and both the dashpot and the operatingmechanism of the circuit-breaker, and while I at present consider the illustrated form of embodiment of my invention to be a preferred form, I wish it to be understood that such illustration is only illustrative, and that various changes may be made without departing from the essential spirit of my invention, at least in its broader aspects. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

VI claim as my invention:

1. A time-delayed drop-out mechanism comprising a clapper-type electromagnet having an electromagnet-frame and a movable armaturearm having a frame-engaging armature-portion, means for biasing said armature-arm toward an open position in opposition to the electromagnetic attraction, time-delay means for delaying the early stages of the opening-movement of the armature-arm, said time-delay means comprising a. suction-type dashpot having relatively stationary and relatively movable normally-seated and substantially-contacting I suction-surfaces, and loose-connection means connecting the movable element of said dashpot with said movable armature-arm in such manner that, when the armature-portion of the armature-arm is released by its electromagnet-i'rame, the loose- A connection of the loose-connection means permits the armature-arm to move substantially unimpededly a very slight amount away from its seated engagement with the electromagnet-frame, whereupon the movable element of the dashpot restrains the further movement of said armature-arm until the suction-action is substantially broken at said suction-surfaces, after which the dashpot permits the armature-arm to again move substantially unimpededly whereby the armature-arm effects a rapid flying-open movement in the rest of its opening-movement away from the electromagnet-frame.

2. A time-delayed drop-out mechanism comprising a clapper-type electromagnet having an electromagnet-frame and a movable armaturearm having a frame-engaging armature-portion, means for biasing said armature-arm toward an open position in opposition to the electromagnetic attraction, time-delay means for delaying the early stages of the opening-movement of the armature-arm, said time-delay means comprising a suction-type dashpot having relatively stationary and relatively movable normally-seated and substantially-contacting suction-surfaces, a movable-element stem attached to said relatively movable suction-surface member and having a substantially rectilinear movement in a line at substantially right angles to said suction-surfaces, and loose-connection means connecting the movable-element stem of said dashpot with said movable armature-arm in such manner that, when the armature-portion of the armature-arm is seated against its electromagnet-frame, the loose-connection means transmits a force from the electromagnet to the dashpot whereby the two substantially contacting suction-surfaces are pressed together, the loose-connection of the loose-connection means permitting the armature-arm to move substantially unimpededly a very slight amount away from its seated engagement with vthe electromagnet-frame, whereupon the movable element of the dashpot restrains the further movement of said armature-arm until the suctionaction is substantially broken at said suctionsurfaces, after which the dashpot permits the armature-arm to again move substantially unimpededly whereby the armature-arm effects a rapid dying-open movement in the rest of its opening-movement away from the electromagnet-frame, the loose-connection means between the armature-arm and the stem being such as to produce substantially no force-reaction on the stem in any direction other than the aforesaid line of movement thereof during the suctionoperation of said dashpot.

3. A'time-delayed drop-out mechanism comprising a. clapper-type electromagnet having an electromagnet-frame and a movable armaturearm having a frame-engaging armature-portion, means for biasing said armature-arm toward an open position in opposition to the electromagnetic attraction, time-delay means for delaying the early stages of the opening-movement of the armature-arm, said time-delay means comprising a suction-type dashpot having relatively stationary and relatively movable normally-seated and substantially-contacting suction-surfaces, and yieldable loose-connection means connecting the movable element of said dashpot with said movable armature-arm in such manner that, when the armature-portion of the armature-arm is seated against its electromagnet-frame, the loose-connection means transmits a force from the electromagnet to the dashpot whereby there is a relatively small resilient reaction between the armature-arm and the movable element of the dashpot yieldably pressing said suction-surfaces together, the loose-connection of the loose-connection means permitting the armature-arm to move substantially unimpededly a very slight amount away from its seated engagement with the electromagnet-frame, whereupon the movable element of the dashpot restrains the further movement of said armature-arm until the suction action is substantially broken, after which the dashpot permits the armature-arm to again move substantially unimpededly whereby the armature-arm effects a rapid flying-open movement in the rest of its opening-movement away from the electromagnet-frame.

4. Tripping-means for releasing the holdingmeans of the mechanism yof a circuit-breaker, comprising the combination, with said breaker,

of a time-delayed undervoltage-responsive mechanism comprising a clapper-type electromagnet having an electromagnet-frame and a movable armature-arm having a frame-engaging armature-portion, means for biasing said armaturearm toward an open position in opposition to the electromagnetic attraction, means for causing the flying-open movement of the armature-arm to eiTect the release of said holding-means, timedelay means for delaying the early stages of the opening-movement of the armature-arm, said time-delay means comprising a suction-type dashpot having relatively stationary and relatively movable normally-seated and substantiallycontacting suction-surfaces, and loose-connection means connecting the movable element of said dashpot with said movable armature-arm in such manner that, when the armature-portion of the armature-arm is released by its electromagnet-frame, the loose-connection of the looseconnection means permits the armature-arm to move substantially unimpededly a very slight amount away from its seated engagement with the electromagnet-frame, whereupon the movable element of the dashpot restrains the further movement of said armature-arm until the suction-action is substantially broken at said suction-surfaces, after which the dashpot permits the armature-arm to again move substantially unimpededly whereby the armature-arm effects a rapid flying-open movement in the rest of its opening-movement away from the electromagnet-frame.

5. Tripping-means for releasing the holdingmeans of the mechanism of avcircuit-breaker, comprising the combination, with said breaker, of a time-delayed under-voltage-responsive mechanism comprising a clapper-type electromagnet having. an electromagnet-frarne and a movable armature-arm having a frame-engaging armature-portion, means for biasing said armaturearm toward an open position in opposition to the electromagnetic attraction, means for causing the flying-open movement of the armature-arm to effect the release of said holding-means, timedelay means for delaying the early stages of the opening-movement of the armature-arm, said time-delay means comprising a suction-type dashpot having relatively stationary and relatively movable normally-seated and substantiallycontacting suction-surfaces, a movable-element stem attached to said relatively movable suctionsurface member and having a substantially rectilinear movement in a line at substantially right angles to said suction-surfaces, and loose-connection means connecting the movable-element stem of said dashpot with said movable armaturearm in such manner that, when the armatureportion of the armature-arm is seated against its electromagnet-frame, the loose-connection means transmits a force from the electromagnet to the dashpot whereby the two substantially contacting suction-surfaces are pressed together, the loose-connection of the loose-connection means permitting the armature-arm to move substantially unimpededly a very slight amount away from its seated engagement with the electromagnet-frame, whereupon the movable element of the dashpot restrains the further movement lof said armature-arm until the suction-action is substantially broken at said suction-surfaces, after which the dashpot permits the armaturearm to again move substantially unimpededly whereby the armature-arm effects a rapid flyingopen movement in the rest of its opening-movement away from the electromagnet-frame, the loose-connection means between the armaturearm and the stem being such as to produce substantially no force-reaction on the stem in any direction other than the aforesaid line of movement thereof during the suction-operation of said dashpot.

6. Tripping-means for releasing the holdingmeans of the mechanism of a circuit-breaker, comprising the combination, with said breaker, of a time-delayed undervoltage-responsive mechanism comprising a clapper-type electromagnet having an electromagnet-frame and a movable armature-arm having a frame-engaging armature-portion, means for biasing said armaturearm toward an open position in opposition to the electromagnetic attraction, means for causing the flying-open movement of the armature-arm to effect the release of said holding-means, timedelay means for delaying the early stages of the opening-movement of the armature-arm, said time-delay means comprising a suction-type dashpot having relatively stationary and relatively movable normally-seated and substantiallycontacting suction-surfaces, and yieldable looseconnection means connecting the movable element of said dashpot with said movable armature-arm in such manner that, when the armature-portion of the armature-arm is seated against its electromagnet-frame, the loose-connection means transmits a force from the electromagnet to the dashpot whereby there is a relatively small resilient reaction between the armature-arm and the movable element of the dashpot yieldably pressing said suction-surfaces together, the loose-connection of the loose-connection means permitting the armature-arm to able element of the dashpot restrains the further movement of said armature-arm until the 'suction-action is substantially broken at said suc-l tion-surfaces. after which the dashpot permits 51 net-frame.

the armature-arm to again move substant'iaiy unimpededly whereby the armature-arm effects' a rapid flying-open movement in the rest of its' opening-movement away from the electromag- JoHN. W. MAY. 

